1. Field of the Invention
The present invention relates to a performance line display unit which displays an image photographed by an imaging device attached near the leading end of a boom of a crane with a performance line of a crane overlapped.
2. Description of the Related Art
A camera system is conventionally known, which overlaps a guide line illustrating a moving range of a leading end portion of a boom on an image photographed by a camera provided to photograph a periphery of a crane and displays its image (refer to Japanese Patent Application Publication No. 2008-312004).
A safety mechanism for a crane is also known, which displays on a display a stable zone and unstable zone with a rotation axis position of a boom as a center (refer to Japanese Patent Application Publication No. H08-29917).
The above-described camera system is configured to obtain a radius of a circle provided by the leading end portion of the boom in the rotation movement at a derricking angle with the present length of the boom, obtain the position of the circle on the world coordinate system based on the radius, projection-transform the position of the circle to the coordinate system of the imaging surface of the camera, overlap the transformed circle on the photographed image of the display as a guide line, and display its image.
A range closer to the crane than the guide line displayed on the display is a safe condition range. An operator rotates the boom while carefully watching whether or not an obstacle is in the safe condition range.
The above-described safety mechanism for a crane is configured to display on a display screen a rotation axis of a crane, a rectangular frame illustrating a crane, a position of each outrigger jack and an operation limit range according to each suspended load W.
However, the above-described camera system has a problem in that it can not determine how far a suspended load can be moved within the operation limit range of the crane if the boom is extended and the derricking angle is reduced because the above-described camera system can only display the moving range of the suspended load at the present derricking angle in the present length of the boom.
Moreover, the above-described safety mechanism for a crane also has a problem in that it can not determine how much the suspended load can be moved on the actually photographed image because the safety mechanism can only display on a display screen only the rotation axis position of a crane, the rectangular frame illustrating a crane and the operation limit line with the rotation axis position as a center.